This invention relates to polyimide ammonium salts that are photocrosslinkable. In particular, it relates to novel polyimides having pendant ammonium carboxylate groups that contain ethylenic unsaturation, and to their preparation and use.
Polyimides are used in the semiconductor industry as dielectric coatings on silicon chips. In the conventional process for making the coatings, a substrate is coated with a solution of a photocrosslinkable polyamic acid. The solvent is evaporated and the polyamic acid is crosslinked with actinic light to insolubilize it. The uncrosslinked portions are washed away with solvent and the remaining polyamic acid is heated to imidize it.
In a second method for forming a polyimide coating on a silicon chip, a solution of a soluble photocrosslinkable polyimide in an organic solvent is prepared and spread on the substrate. The solvent is evaporated and the polyimide is crosslinked and insolubilized with actinic light. Portions that were not exposed to the light are then washed away with the solvent. In both methods, a diamine containing an ethylenically unsaturation group is used as a monomer in preparing the polyimide to make it photocrosslinkable.